Research at Washington University Mass Spectrometry Resource plans: 1. to provide wide range low resolution GCMS service to local, regional, national, and international biomedical investigators 2. to provide expert technical assistance, analytical services, and interpretive advice on high precision GCMS selected ion monitoring quantitation (SIM-GCMS) of substrate content and stable isotope enrichment in physiologic samples. 3. To provide a fully automated isotope ratio mass spectrometer (IRMS) for rapid, high sample volume operation for measurement of stable isotope enrichment in expired and excreted end products of endogenous substrate metabolism. 4. To develop an isotope ratio monitoring GCMS (IRM-GCMS) for high precision quantitative stable isotope analysis with smaller sample size and less sample preparation than with IRMS and with the ability to measure greater tracer dilution than possible with SIM-GCMS. 5. To establish a high resolution mass spectrometry-fast atom ionization facility for the analysis of high molecular weight or thermally labile molecules. 6. To develop a facility for HPLC-thermospray mass spectrometry to augment conventional methods for peptide sequencing and establish other HPLC-MS analyses. 7. To make the newly developed facilities available for use by qualified investigators at the local, regional, national, and international levels.